A Hall sensor array for internal current profile constraint

• Published in: Review of scientific instruments Vol. 81; no. 10; p. 10E105
• Main Authors: Bongard, M W, Fonck, R J, Lewicki, B T, Redd, A J
• Format: Journal Article
• Language: English
• Published: United States 01.10.2010
• ISSN: 1089-7623
• DOI: 10.1063/1.3475539

Measurements of the internal distribution of B in magnetically confined plasmas are required to obtain current profiles via equilibrium reconstruction with sufficient accuracy to challenge stability theory. A 16-channel linear array of InSb Hall effect sensors with 7.5 mm spatial resolution has been constructed to directly measure internal B(z)(R,t) for determination of J(ψ,t) associated with edge-localized peeling mode instabilities in the Pegasus Toroidal Experiment. The diagnostic is mounted in an electrically isolated vacuum assembly which presents a slim, cylindrical profile (∼1 cm outside diameter) to the plasma using graphite as a low-Z plasma facing component. Absolute calibration of the sensors is determined via in situ cross-calibration against existing magnetic pickup coils. Present channel sensitivities are of order of 0.25 mT. Internal measurements with bandwidth of ≤25 kHz have been obtained without measurable plasma perturbation. They resolve n=1 internal magnetohydrodynamics and indicate systematic variation in J(ψ) under different stability conditions.